Process for the production of a composite component that can resist high thermal stress

Abstract

The invention provides a process for the production of a composite structural part which can withstand high thermal stress, consisting of at least one graphite part and at least one metal part made of a hardenable copper alloy. In accordance with the invention, the metal part is bonded, by a hot isostatic press process, with the graphite part, which has a layer made of copper or a copper alloy on the bonding surface. In this way, it is possible to use copper-chromium-zirconium alloys with more complex composite structural part constructions and with thin-wall parts of the metal component, without the good mechanical characteristics of the copper-chromium-zirconium alloy being destroyed.

Description

BACKGROUND OF THE INVENTIONThe present invention relates to a process for the production of a composite component that can resist high thermal stress. The composite comprises at least one graphite part and at least one metal part made of a hardenable copper alloy, which is surface-bonded to the graphite part.As a result of its special characteristics, such as high thermal stress capacity, good thermal conductivity, and low pulverization rate, graphite is very suitable for structural parts that are under strong thermal stress. Graphite is used in very different forms, such as polycrystalline graphite, pyrolytic graphite, or even fiber-reinforced graphite. A disadvantage of graphite is that it has only limited mechanical strength and ductility in the fiber-reinforced form. Moreover, because of leakage, the porosity of the graphite generally prohibits direct contact with liquids, such as is necessary for sufficient dissipation of heat with actively cooled thermal shields. Therefore, as...

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Benefits of technology

imately 900.degree. C., without disadvantageous effects on its mechanical characteristics, so that parts made of this alloy can be bonded with parts made of graphite.

One disadvantage of this copper alloy is that its fracture toughness drops below a critical minimum with neutron stress, so that it is suitable, in only a qualified manner, for structural parts which are to be used in fusion reactors.

Other known copper alloys which have optimal high-temperature strength characteristics are hardenable copper-chromium-zirconium alloys made of approximately 0.3-1.2 wt % chromium, 0.03-0.3 wt % zirconium, and the remainder, copper.

In comparison to dispersion-reinforced copper alloys, these alloys have, above all, substantially better values for fracture toughness after neutron stress, so that they are basically very suitable for structural parts used in fusion reactors.

Copper-chromium-zirconium alloys are hardenable alloys that attain their good characteristics with respect to strength and elongation by a special process during production and by a final hardening cycle at approximately 500.degree. C. In order to retain these good characteristics in the hardened state, these alloys should not exceed the hardening temperature of 500.degree. C. in further processing, in particular, during the bonding with the parts made of graphite or in use, since otherwise, fatigue of the alloy occurs and strength values rapidly decline.

Thus, the known high-temperature soldering for the bonding of parts made of this alloy with graphite parts is practically out of the question. One possibility of bonding graphite with parts made of high-strength copper alloys, among others also, made of copper-chromium-zirconium alloys, without damaging the rigidity of the composite structural parts by the bonding process, is the use of electron beam welding, as it is described, for example, in EP 0 741 116 A1. One disadvantage of that process is that it is only suitable for parts made of copper-chromium-zirconium alloys having a relatively large wall thickness. In the case of structural parts with thin walls, the heat, which appears during the electron beam welding and is, in fact, relatively low, is still too great to rule out a decline in the good mechanical characteristics of the copper-chromium-zirconium alloy. Moreover, especially with more complex structural parts, for example, with actively cooled installations, where several graphite parts must be bonded in several planes with cooling agent conduits, electron beam welding cannot be used frequently because of an insufficient accessibility of the surfaces to be bonded.

Problems solved by technology

A disadvantage of graphite is that it has only limited mechanical strength and ductility in the fiber-reinforced form.

The disadvantage of such composite structural parts which use molybdenum as a material for the metal parts are the relatively high costs and the difficulty in processing and welding molybdenum.

One disadvantage of this copper alloy is that its fracture toughness drops below a critical minimum with neutron stress, so that it is suitable, in only a qualified manner, for structural parts which are to be used in fusion reactors.

One disadvantage of that process is that it is only suitable for parts made of copper-chromium-zirconium alloys having a relatively large wall thickness.

In the case of structural parts with thin walls, the heat, which appears during the electron beam welding and is, in fact, relatively low, is still too great to rule out a decline in the good mechanical characteristics of the copper-chromium-zirconium alloy.

Moreover, especially with more complex structural parts, for example, with actively cooled installations, where several graphite parts must be bonded in several planes with cooling agent conduits, electron beam welding cannot be used frequently because of an insufficient accessibility of the surfaces to be bonded.